The present invention relates to a color-converting/filter substrate that enables multi-color display with high detail and is excellent in terms of environmental resistance and productivity, and a multi-color organic luminescent display device having the color-converting/filter substrate. More specifically, the present invention relates to a color-converting/filter substrate for display use in image sensors, personal computers, word processors, televisions, facsimiles, audio equipment, video equipment, car navigation equipment, desk-top electronic calculators, telephones, mobile terminal equipment, industrial measuring equipment, and so on, and a multi-color organic luminescent display device having the color-converting/filter substrate. In particular, the present invention relates to a multi-color organic EL display panel that uses a color conversion method.
In recent years, there have been rapid advances in the diversification of information. Amid this, ‘attractiveness, lightness, thinness, and excellent performance’ have come to be demanded of display devices in the information field, and development has been carried out vigorously with an aim of further reducing power consumption and making devices that respond faster. In particular, ideas on high-detail full-color display devices have been widely put forward.
A laminate type organic electroluminescence (hereinafter referred to as ‘organic EL’) device that has an organic molecule thin-film layered structure, emits light with a high brightness of 1000 cd/m2 or more at an applied voltage of 10V, and is superior to liquid crystal display devices and so on in terms of viewing angle dependence, fast response and so on, was reported by Tang et al. in 1987 (Appl. Phys. Lett., 51, 913), and ever since research with an aim of making organic EL devices fit for practical use has been vigorously carried pursued. Moreover, the development of similar devices using organic polymeric materials has also been vigorously pursued carried out.
With organic EL devices, a high current density can be realized at a low voltage, and hence emitted light brightness and light emission efficiency can be expected to be higher than with inorganic EL devices or LEDs. Moreover, organic EL devices have excellent characteristics as display devices, for example (1) high brightness and high contrast, (2) low-voltage driving and high light emission efficiency, (3) high resolution, (4) wide angle of visibility, (5) high response speed, (6) realization of high-detail, multi-color display, and (7) lightness and thinness. Due to these points, application to flat panel displays that have ‘attractiveness, lightness, thinness, and excellent performance’ can be anticipated.
Green monochrome organic EL display panels for installation in automobiles and the like were commercialized by the company Pioneer in November 1997. There is now a rush to make fit for practical use multi-color organic EL display panels that have long-term stability and fast response, and are capable of high-detail multi-color or full-color display, this being to answer to the diversifying needs of society in the future.
One example of a method of making organic EL display panels be multi-color or full-color is a method in which light emitters of the three primary colors red (R), green (G) and blue (B) are arranged separated from one another in a matrix, and are each made to emit light (see Japanese Patent Application Laid-open No. 57-157487, Japanese Patent Application Laid-open No. 58-147989, Japanese Patent Application Laid-open No. 3-214593, etc.). With this method, light-emitting materials of the three types red, green and blue must be arranged with high precision in a matrix, and hence this is technically difficult, and moreover manufacture cannot be carried out cheaply. In addition, there are drawbacks such as the color shifting upon prolonged usage due to the lifetime (the brightness change characteristic) differing between the three types of light-emitting material.
Moreover, a method in which colored filters are used with a backlight that emits white light, thus transmitting the three primary colors is also known (see Japanese Patent Application Laid-open No. 1-315988, Japanese Patent Application Laid-open No. 2-273496, Japanese Patent Application Laid-open No. 3-194885, etc.). However, an organic EL light emitter that emits white light of a sufficiently high brightness and has a sufficiently long lifetime for obtaining red, green and blue light of high brightness has not yet been obtained.
Moreover, a method in which fluorescent bodies that are arranged separated from one another in a plane are made to absorb light emitted from a light emitter, and hence fluorescence of a plurality of colors is emitted from the fluorescent bodies is also known (see Japanese Patent Application Laid-open No. 3-152897, etc.). Such a method has been used with CRTs, plasma displays, and so on.
Moreover, in recent years, a color conversion method in which fluorescent materials that absorb light in the emission region of an organic EL light emitter and then emit fluorescence in the visible region are used in filters has been disclosed (See, Japanese Patent Application Laid-open No. 5-258860, etc.). The color of the light emitted by the organic EL light emitter is not limited to being white, and hence an organic EL light emitter having a higher brightness can be used as the light source; in the case of a color conversion method in which an organic EL light emitter that emits blue light is used (Japanese Patent Application Laid-open No. 3-152897, Japanese Patent Application Laid-open No. 8-286033, Japanese Patent Application Laid-open No. 9-208944, etc.), the blue light is subjected to wavelength conversion into green light and red light. If color-converting/filters containing such fluorescent colorants are patterned with high detail, then a luminescent-type display that is full-color despite using low-energy radiation such as near ultraviolet light or visible light from a light emitter can be constructed.
Examples of the method of patterning the color-converting/filters include (1) a method in which, as in the case of an inorganic fluorescent body, a fluorescent colorant is dispersed in a liquid resist (photoreactive polymer), a film thereof is formed using a spin coating method or the like, and then patterning is carried out using a photolithography method (Japanese Patent Application Laid-open No. 5-198921, Japanese Patent Application Laid-open No. 5-258860), and (2) a method in which a fluorescent colorant or fluorescent pigment is dispersed in a basic binder, and then this is etched using an acidic aqueous solution (Japanese Patent Application Laid-open No. 9-208944).
Important issues with regard to the practical use of an organic EL light emitter in a multi-color display panel are having a high-detail multi-color display capability, and having long-term stability with regard to color reproducibility and so on (see Kino Zairyo (‘Functional Materials’), Vol. 18, No. 2, page 96). However, with multi-color organic EL display panels, there is a drawback that after driving for a certain time, there is a marked deterioration in the current-brightness characteristic.
A typical cause of this deterioration in light emission characteristics is the growth of dark spots. Dark spots are points where there is a defect in light emission. As oxidation progresses during driving or storage, the growth of dark spots progresses, and the dark spots spread over the whole of the light-emitting surface. It is thought that such dark spots are caused by oxidation or agglomeration of the layered materials constituting the light emitter due to oxygen or moisture in the light emitter. The growth of dark spots progresses not only during passing of a current, but also during storage, and is thought, in particular, to be (1) accelerated by oxygen or moisture present around the light emitter, (2) affected by oxygen or moisture present as an adsorbate in the organic layered films, and (3) affected also by moisture adsorbed on components when producing the light emitter or by the infiltration of moisture during manufacture or the like.
The typical sectional structure of a color conversion type multi-color organic EL display panel is shown in FIG. 1. Color-converting/filter layers 22 to 24 of three types are formed on a supporting substrate 21, and a polymeric film layer 25 covers the color-converting/filter layers 22 to 24, with an upper surface of the polymeric film layer 25 being made to be flat. Furthermore, transparent electrodes (anodes) 26, a hole injection layer 27, a hole transport layer 28, a light-emitting layer 29, a hole injection layer 30, and cathodes 31 are formed on the polymeric film layer 25. Here, as shown in FIG. 1, the color-converting/filter layers 22, 23 and 24 are provided below the transparent electrodes 26. As mentioned above, the color-converting/filter layers each comprise a resin having color-converting colorant (s) mixed therein. Moreover, due to the problem of the thermal stability of the colorant (s) mixed in, drying cannot be carried out at a temperature above 200° C., and hence there is a high possibility of the color-converting/filter layers being formed in a state in which moisture contained in the application liquid or moisture that has got in during the pattern formation step is still held. Such moisture held in the color-converting/filter layers passes through the polymeric film layer and reaches the light emitter during storage or driving, and is a factor in the growth of dark spots being promoted.
As a method of preventing such moisture from infiltrating in to the organic EL light emitter, art is known in which an insulating inorganic oxide film layer is provided to a thickness of 0.01 to 200 μm between the color-converting/filter layers and the organic EL light emitter (i.e. between the polymeric film layer 25 and the transparent electrodes 26 or the hole injection layer 27 in FIG. 1) (Japanese Patent Application Laid-open No. 8-279394). The inorganic oxide film layer is required to have high moisture resistance for maintaining the life of the organic light-emitting layer. Specifically, it is considered to be preferable for the gas permeability coefficients for water vapor and oxygen of the inorganic oxide film layer to both be not more than 10−13 cc·cm/cm2·s·cmHg (according to the gas permeability test method of JIS K7126).
Moreover, as shown in Japanese Patent Application Laid-open No. 7-146480 or Japanese Patent Application Laid-open No. 10-10518, as a method of forming an inorganic film layer, there is a method in which SiOx or SiNx is formed by DC sputtering on the polymeric film layer that has been formed on the colored filter layers, and there is known to be an effect of improving the adhesion of the transparent electrodes. Moreover, there is also a method in which low-melting-point glass is sintered (Japanese Patent Application Laid-open No. 2000-214318).
Regarding the deterioration of the performance of the organic EL light emitter, research has been carried out vigorously in various places, and up to now a variety of causes have been announced. One of these is that organic EL layers such as a light-emitting layer are made from a material having low heat resistance, and hence deterioration of the performance due to heat generated during driving of the light emitter is a serious problem.
As described above, with a color conversion type multi-color organic EL display panel, in addition to having a function of preventing moisture held in the color-converting layers from passing through the polymeric film layer and reaching the light emitter during storage or driving, which is a factor in the growth of dark spots being promoted, it is also necessary to efficiently disperse to the surroundings heat generated through driving the light emitter, thus keeping the temperature of the color-converting layers and the light emitter low and hence preventing deterioration thereof.
Moreover, it is necessary to form the inorganic film layer with good adhesion to the polymeric film layer so as to be able to cope with large changes in the driving environment, i.e. the temperature and humidity.
In view of the problems described above, it is desirable to provide a multi-color organic EL display panel for which stable light emission characteristics are maintained over a prolonged period, and to realize a method for efficiently forming such a multi-color organic EL display panel.